Essay:Quantum entanglement

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A Youtube video talks about entanglement (and seriously fucks up QM interpretations with observational/instrumentalist facts about QM). I decide to jump in with a minor correction.


Quick point. You said during the entanglement part that it seems like information is travelling faster than the speed of light. Entanglement emphatically does not transmit information faster than light. The entangled pair start as unknown to the observer and then both collapse once observed. To send information you have to specifically encode a spin into one particle. You can't do this because you'd have to observe them first, which destroys the entanglement; leaving you with just randomness.

The above is why you can't have superluminal communication. Quantum collapse from a superpositional state is a statistical and probabilistic process. In order to convey infomation, you cannot have a random process, it must be controlled. This is also tangled up in how information and entropy works. The youtube user who uploaded the video responds with "hence I said it seems to" - but I disagree, there's no "seems to" about it, it Just. Fucking. Doesn't.

Months pass, and I discover this while clearing my inbox out.

Shit for brains:

Information can still travel faster than light. Think of a coin, you spin it on a table. Then place 2 pieces of glass vertically on it's side (while its still spinning). Also have 2 cameras (A&B) on each side recording the spinning coin and beaming the video live via fire-optic cable to 2 different locations, X & Y, extremely far apart (eg 600,000km) You then clamp the spinning coin between the glasses. [...] Location X or Y would see the recorded side of the coin facing it, either Head or Tail. If there is no observer at both location, the probability of seeing a Head or Tail side of the coin at both location is 50%-50%. But once an observation has been made, lets say at location X, the observer seeing the Head side would instantly KNOW that whoever watches at location Y must be seeing the Tail side of the coin. Being at 600,000km apart (twice the speed of light), this information travelled faster.

This was broken into two comments, though I figured out what they were saying from the first one alone. This thought experiment doesn't describe the transfer of information from X to Y, as the knowledge of what is at Y is sent to X already encoded as information. Okay, so sometimes I can be a complete arsehole on the internet:


I cannot see this being anything but "not even wrong".

Note that this was written in response to the first comment (prior to the [...] above) due to YouTube's crappy system making it difficult to keep track.

Shit for brains:

care to elaborate?


A full description of information theory won't fit in a YouTube comment, so let's just take the very informal definition of it being "how surprised you are" by a result. If your camera at X sees heads, then an observer there isn't surprised at all that camera Y sees tails. The information of what Y sees is encoded in the same signal that X sees. Information isn't transferred faster than light.

A far longer description can be found here, written by Richard Dawkins as an answer to "give an example of a mutation which increases information in the genome".

This isn't dicking about with defintions to be proved right, if you don't know what "information" actually is in a well-defined sense, then you simply cannot talk about information transfer in a coherent and useful way. Hence how information theory is formulated to convey complexity and information transfer. Dawkins had this problem with the fact that a creationist wouldn't be able to get a sound-bite answer to their question; a colloquial vision of "information" just doesn't cut it.

Again, the reasoning is all bound up in entropy and energy, which is why information is subject to restrictions placed upon it by special relativity.

Shit for brains:

When X KNOWS what Y is seeing instantly and vice versa, it is an information. And their distant is so far apart that this knowledge travelled faster than light.


No, information has not travelled faster than light. Look up what information actually *is*. You cannot use a completely wrong definition of information and say that travels faster than light.

Shit for brains:

Oh yea? How about this, we play a game of coin flipping, Heads up you win, tails i win. Before i release my hand to review the result, there is no information on who won. But now, after release my hand to show the coin, isn't information made available now on who won? Also, i was using video 'signal' as an example. In absolute reality, entangled particles miles apart do not need present-world signals to tell each other to behave. Hidden variable beyond our dimension makes the effect INSTANT.

This is where digital physics advocates leave reality behind. I'm not entirely sure what this is even supposed to prove... if you view a coin in someone's hand, the "information" of whether it's heads or tails travels to your eyes via light, at light speed, not faster. If the last part implies that they're a hidden variables advocate, then I'd assume they'd know that information transfer cannot take place faster than light. HV has it's strengths and weaknesses but is a bit beyond the scope of this for now.


That isn't transfer of information. Look up what information actually *is* and then what is required for information to be transferred. No, it doesn't travel faster than light in any of those cases.

What's more likely -- that you have uncovered fundamental flaws in this field that no one in it has ever thought about, or that you need to read a little more? Hint: it's the one that involves less work.

How many times do you have to tell someone to look up information theory before commenting on information transfer? I figured the shameless xkcd quote would be relevant.

Shit for brains:

I dont know if u're just trolling or ever been to a science class. Quantum entanglement is real and you probably should look up on 'hidden variables', 'nonlocal information' and 'meta information'. You probably still think that rules outside our classical dimension must not be violated beyond the quantum dimension. Poor kid.

If anyone can point to where I said "quantum entanglement isn't real" do let me know. Trolling? Me?


Unfortunately, I got my information on quantum mechanics through doing quantum chemistry, studying physics and perusing a doctorate that requires extensive knowledge of quantum physics, including superpositional and entangled spin states - and not through bad pop science documentaries or YouTube clips. You are using an ill-conceived and loose description of "information" when you say "information travels faster than light", making all your thought experiments nothing but trivial.

Most of this is true. An aspect of my research is parahydrogen induced polarisation. p-H2 is a superpositional spin state of the H2 molecule that exists because H2 is symmetrical. Because of symmetry, the spin combinations of up-down and down-up are indistinguishable. This generates two states represented mathematically by "up-down PLUS down-up" and "up-down MINUS down-up" (it's the latter that constitutes the singlet state of p-H2, the former is part of the triplet o-H2 manifold). These are superpositions, and the fates of the proton spins are now entangled because of the symmetry. It's not possible to separate the H2 molecule homolytically and preserve the entanglement in order to send them to far flung corners of the universe, which is how we're used to hearing about entanglement, but the underlying principle is absolutely identical. When you react H2 in one of these states to form an asymmetrical metal dihydride complex (among other compounds), they resolve ("quantum collapse" for those who like their QM jargon) into two states of "up-down" and "down-up" ("up-up" and "down-down" can't come from these states; entanglement and conservation of momentum see to that) and it's from this that we derive hyperpolarised enhancement because the selective spin populations align the overall magnetic moment of the sample. This is a real application of entanglement and superpositional quantum collapse. If the effect didn't occur then we wouldn't get hyperpolarisation and everything would go to an equilibrium distribution of spin states instantly, rather than as a result of normal spin-allowed relaxation processes. As I see this almost every day, it's a bit rich to assume that I'm denying entanglement exists. The sad part is that Shit For Brains has probably come away from this discussion thinking I'm some closed-minded fool while their internet derived knowledge of digital physics and their trivial thought experiments on superluminal information transfer are correct. Alas, nothing I could possibly say would change that particular opinion.

TL;DR: I know what the fuck I'm talking about.

Shit for brains:

Yes it is indeed 'unfortunate' for u that inspite of years of 'EXTENTSIVE' studies, you have yet to provide a clear cut solution and explaination of how to unify both quantum and classical physics, despite them co-exisiting. How does ur knowledge that proves nothing be anything less 'trivia' than mine? Smart ass

Where this came from I have no idea. If you can see where I've said I aim to marry classical and quantum physics (for the record, my opinion is that you don't need to because it is a severe error to assume the quantum world is classical underneath) please point it out.


What are you on about now? You were trying to show that information travels faster than light - something with neither quantum theory nor relativity allow - using a poor definition of "information" and with thought-experiments that showed nothing but trivial inference because you don't seem familiar with information theory. That was what was under discussion, not marrying QM and relativity and/or classical physics.

As I'm not sure you're capable of reading, I consider this exchange complete.

See this flow chart for a better description. Anyway, despite bowing out, another reply is forthcoming:

Shit for brains:

Simple, 1) u were belittling 'thought experiments'. Don't do that. Countless discoveries and investigations sprang from thought-experiments. Einstein himself began lots of works from thought experiments. 2) youtube videos of quantum physics are not less credible. Or else why the hell are u here? 3) i was giving an example on how i believe information can travel faster than light beyond classical laws. U dont like my example, shut up & go back to ur cave. One day i'll prove u wrong.

Now, I'm not replying to this, I've already bowed out on grounds of "this looks good on your CV, not so much on mine". However, I cannot resist just finishing it off here instead.

If you are going to use terrible thought experiments, I will belittle them. They still need to be well-formed and, for lack of any better word, correct. After all, all of mathematics is, in effect, a thought-experiment which derives more complicated ideas from simple axioms. If those thought-experiments don't work, they are wrong. The entire point of thought experiments in physics is to build models of reality which you can then later test. In fact, simple thought experiments based on models of quantum collapse in a probabilistic manner demonstrate why you cannot use entanglement to send information faster than light. Einstein used thought-experiments extensively, but they always lead to "what if" scenarios. Such thought experiments began "does a falling person feel their own weight?" which triggered general relativity - the thought experiment proposed a scenario that was expanded and extrapolated into real experimental data and theory. Not least orbital motion, light diffraction by gravity, measurements of time dilation in short-lived in particle accelerators, and GPS calibration all back up relativity. Meanwhile, the above "spinning coin" experiments can be disproved with a simple question: is there a way for X to send Y a message faster than light? Can X send Y the signal for "heads" - deliberately and controlled - faster than light? Try it. You'll struggle.

Anyway, if Shit For Brains can prove me wrong as claimed, I'll be here, in my cave, doing some real science and waiting. I would really love to be proved wrong on this, because if you can demonstrate that quantum entanglement violates special relativity by transferring information faster than light then the Institute of Physics and the Nobel Prize Committee would love to hear from you.